There is significant number of patents, especially, the USA patents, which describe different constructions of cryosurgical probes and catheters. An aim of these patents is to solve some main problems, which are common to cryosurgical probes and catheters.
The problems include construction of relatively cheap and simple probes or catheters with high reliability and sufficiently effective thermal insulation of their lateral non-operating walls. Besides, cryosurgical catheters must have high flexibility, especially, when they are used for cardiac interventions. At the same time the closed distal end (cryotip) of such probe or catheter must provide in many cases high specific freezing capacity at sufficiently low-temperatures.
Analysis of USA patents related to this field shows, that constructions of the proposed probes and catheters intended for cryosurgery do not conform the above-mentioned requirements.
For example, U.S. Pat. No. 3,971,383 proposes a cryogenic surgical instrument with a coaxial assembly of the flexible lumens; the inner one being connected to a supply of cryogenic liquid, and the space between the outer wall of the inner lumen and the next lumen forming a return line for evaporated cryogenic liquid which is vented to the atmosphere; and the space between the outermost one of the coaxial lumens and the intermediate lumen containing a gas, such as normal butane, serving for thermal insulation of the inner and intermediate lumens.
U.S. Pat. No. 5,716,353 describes a probe for cryosurgery which consists of three lumens: an inner lumen for supply a cryogenic refrigerant to a cryotip positioned on the distal end of an outer jacket lumen, and an intermediate lumen situated concentrically around the inner lumen. The channel between the inner and intermediate lumens serves as a venting path for venting cryogenic refrigerant from the freezing zone. This construction is simple, but it does not provide sufficient thermal insulation as required in construction of a cryogenic catheter. Consequently, it may cause over-heating of the venting cryogenic refrigerant, as well as over-cooling of tissues adjacent the intermediate section of the catheter.
U.S. Pat. No. 5,573,532 describes design of a cryosurgical instrument, which comprises lumens of cryogenic fluid supply and return of cryogenic fluid vapors; these lumens are situated concentrically and the return lumen is sealed with a cryotip. The patent proposes to do vacuum insulation of the return lumen. Such construction is very expensive and has low reliability. Besides, this vacuum insulation limits flexibility of the probe, especially, when it has significant length and is used as a catheter.
U.S. Pat. No. 5,674,218 describes a cryosurgical instrument, a system and method of cryosurgery. According to this patent a cryogenic liquid (preferably, liquid nitrogen) is preliminary sub-cooled below its normal boiling point and in such condition it is supplied into the open proximal end of the internal supply line. The outer lumen of the cryosurgical instrument is provided with active vacuum insulation.
Obviously, this construction cannot ensure high flexibility and cannot be used as the base for construction of a catheter for cryosurgery.
U.S. Pat. No. 5,254,116 describes a cryocatheter with a set of vent holes in the lateral wall of a central feeding lumen; besides, sub-cooled liquid nitrogen is delivered into the central feeding lumen as a cryogenic liquid. This construction does not ensure proper thermal insulation of the cryocatheter.